It is generally recognized that light-induced reactions may have a deleterious effect on the quality of a variety of foods, especially those foods containing fat. This problem has become more pronounced in recent years with the advent of high intensity fluorescent lights for illumination of display cases in supermarkets and convenience stores.
Flavor changes in milk after exposure to light has been repeatedly described in the literature. Reported results are confusing, but there is apparent agreement that
A. OXIDIZED AND SUNLIGHT FLAVOR ARE THE TWO PRINCIPAL OFF-FLAVORS INDUCED BY LIGHT,
B. THE WAVELENGTHS OF LIGHT INDUCING THE OFF-FLAVOR REACTIONS ARE WITHIN THE RANGE OF THE VISIBLE SPECTRUM, SPECIFICALLY 380 TO 750 NM,
C. THE ABSENCE OF AIR RETARDS OFF-FLAVOR DEVELOPMENT; AND
D. RIBOFLAVIN AND TRYPTOPHANE DESTRUCTION ARE DIRECTLY RELATED TO THE FLAVOR DEFECT.
See the article entitled "Controlling Light Activated Flavor In Milk" by M. E. Gregory, A. P. Hansen and L. W. Aurand appearing in a North Carolina Food Extension Service Pamphlet entitled "Timely Tips" dated November, 1970.
The effect of artificial light on milk has gained wide attention in recent years with the increasing popularity of all-plastic containers. These all-plastic containers which may be clear or opaque generally suffer from the same deficiency as glass containers with respect to light transmittance characteristics. Thus, as compared to plastic-coated paper containers, such all-plastic containers absorb or filter out less of the deleterious range of the visible spectrum which in turn generally results in milk packaged in these containers having an off-flavor or oxidized flavor after being exposed to fluorescent light or sunlight for between about 12 to 24 hours.
It is desirous that these all-plastic, milk containers filter out the deleterious range of the visible spectrum and simultaneously be transparent to give the milk an aesthetic and pleasing appearance. Conventional all-plastic, clear containers, such as the polycarbonate containers disclosed in U.S. Pat. No. 2,964,794, are transparent and give the milk an aesthetic and pleasing appearance, but fail to absorb or filter out the deleterious range of the visible spectrum. Conventional plastic-coated paper containers effectively filter out the deleterious range of the visible spectrum, but completely conceal the appearance of the contained milk. Conventional high density polyethylene containers pigmented with titanium dioxide ineffectively filter out or absorb the deleterious range of the visible spectrum and being opaque, fail to give the milk an aesthetic and pleasing appearance.
In order to reduce the light transmission characteristics of an all-plastic container in the 380-750 nm visible spectrum range, it has been proposed to coextrude a laminate consisting of an outer all-plastic layer and an inner black pigmented layer. Such a coextruded laminate is disclosed in J. Inst. Can. Sci. Technol. Aliment, Vol. 6, No. 3,1973 in an article entitled "Effect of Packaging Material on Light Induced Quality Deterioriation of Milk" by Abdus Sattar and John M. deMan. Such a container reduces the transmission to well below 2% in the greater part of the visual spectrum. However, such a coextruded laminate system can only be used to mold a container by extrusion or injecting blow molding techniques if expensive and highly complicated machinery is used. Furthermore, adhesion problems between the plastic and pigmented layer is likely to occur after repeated washings requiring that a third or adhesive layer be blow molded between the plastic and pigmented layer. The requirement of such a third or adhesion layer makes the extrusion or injection blow molding process even more complicated and expensive.
U.S. Pat. No. 2,598,506 discloses a process for inhibiting deleterious photochemical action in packaged, edible dairy products by shielding the products from the harmful light wavelengths of the visible spectrum. The shielding is accomplished by a color screen which may be a lacquer or a laminate applied to the package. Although this shielding process is generally effective for most plastics, it suffers from the shortcomings that the shield may be difficult to lacquer or to laminate to all plastic containers, such as polycarbonate containers, and that once lacquered or laminated to the plastic container, the shield may have a tendency to separate from the container or dissolve after repeated washings of the container in basic or acidic detergent solutions.
In accordance with the present invention, a reusable, polycarbonate container has been developed which filters out the portion of the visible spectrum of from about 380 to 550 nm and which is transparent and gives its contents an aesthetic and pleasing appearance.